OK so I am going to resurrect an old thread. My 1969 911 has an electric fuel pump mounted in the engine compartment. It is feeding a pair of weber carbs so I am running the fuel pressure at 4psi and it is controlled by an adjustable regulator. This was the factory installation so it has been this way for a long time, it is pulling the fuel through rather than pushing.
I am running into a situation where the fuel pressure will intermittently drop to 1.5 to 2 psi. When this happens my wide band o2 sensor will show AFR greater than 15.6.
I am going to relocate the fuel pump and mount it at the base of the tank and push the fuel through vs pull, which is how it is operating now. I am not sure if my pump is failing, if it is sucking air or vapor locking.
After reading this thread and a few others the general consensus is electric pumps operate better when pushing. I know my car came from the factory with the electric pump pulling but the modern fuel blends may be playing a part in the problem.
OK so now the real question, should I add a return line for the tank while I am at it? Is a return line needed on a carb setup? I assume not since it never had one but best to check first.